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400
Democritus (400 B.C.)
Proposed that matter was made up of little particles he called "atomos" -
Antoine Lavosiev
Identified Oxygen and it's role in combustion -
Joseph Proust
Determined that elements in a compound will always combined in the same whole number ratios -
John Dalton
In his book " A New System of Chemical Philosophy," he proposed a new comprehensive atomic theory and propose the Law of Multiple Proportions -
Amadeo Avogadro
Detemined experimentally that equal volumes of gases at the same conditions would contain the same number of particles. -
E. Goldstein
Worked with the "canal Rays" (later known as the cathode rays) and first proposed the existence of a positively charged particle. -
Henri Becquerel
Discovered that some matter could spontaneously emit high energy that exposed photographic plates. -
J.J Thompson
Experimentally determined the existence of both electrons and protons using cathode ray tubes. -
Marie Curie
Along with her husband, she was the first to isolate a radioactive elemant - radium -
Max Planck
Published his "quantum theory" which explains the behavior of sub-atomic particles in an atom -
Albert Einstein
Proved that matter and energy are interchangeable; we summarize his paper in the equation E=mc² -
Robert Milikan
using his famous "oil drop" experiment he confirmed and calculated the charge and mass of an electron -
Lord Rutherford
alaong with Geiger and Marsden, he proved that atoms were mostly empty space with very small positive cores by using the "gold foil" experiment -
Niels Bohr
proposed the "planetary" model of the atom which replaced the "plum pudding" model -
Henry Mosely
working with x-ray analysis of atoms, he determined that the number of protons define an atom's idenity and is equal to the elements atomic number number; he also proposed the concepts of isotopes -
James Chadwick
indentified a third, a neutral, sub-atomic particle.
